updated 09:10 pm EST, Tue February 22, 2011

Researchers did not gauge negative impacts

A new study has reportedly found that cellphone signals cause a measurable change in brain activity where the antenna is held next to a user's head. Researchers admitted that the study, which was conducted by the National Institutes of Health and Brookhaven National Laboratory, did not attempt to gauge potential negative effects of the electromagnetic radiation.

The researchers scanned subjects' brains while cellphones were held to the left and right sides of the head for nearly an hour during two test days. Participants did not speak into the phone or listen to conversations, while the phone was left off on one of the days and muted on the next to prevent users from knowing if the device was powered on or off.

The tests showed an eight to 10 percent rise in glucose metabolism in the brain regions near the active cellphone antenna. The shift was said to be comparable to the changes in glucose metabolism in the visual cortex when someone speaks, according to Dr. Nora Volkow, a researcher who was involved in the study and quoted in a Wall Street Journalreport.

"This study shows that the human brain is sensitive to electromagnetic radiation coming out of cellphones," said Volkow. She cautioned, however, that the findings do not show if the interaction causes harmful side-effects.

The issue has been fiercely debated since the beginnings of widespread cellphone use, though reports disagree on the potential for negative consequences such as cancer. San Francisco recently moved to require mandatory labeling for radiation levels emitted by different handsets, but the legislation has been met with a lawsuit from the CTIA, a trade organization that represents cellphone makers and carriers.

The FCC tests devices to ensure compliance with SAR levels that the agency deems safe. The FDA has also suggested that existing data does not provide conclusive evidence of negative health effects from cellphone radiation.

The latest study has been published this week in the Journal of the American Medical Association.